The present invention relates generally to electrical signal power amplifiers, and, more specifically, to radio frequency (RF) power amplifiers.
Radio frequency transmission of an electrical signal requires corresponding power amplification thereof for the intended transmission range. RF signals typically have a broad frequency spectrum from several megahertz (MHZ) to tens of gigahertz (GHZ), and higher.
RF transmission typically occurs at a single band for specific applications such as cellular phone transmissions. Typical cellular phone transmission bands include 800 MHZ and 1900 MHZ in the United States, and 900 MHZ and 1800 MHZ in most countries in Europe and Asia.
Portable cellular phones are being developed in ever decreasing size for convenience of use. Correspondingly, the electrical components thereof must also decrease in size while still providing effective transmission performance. However, the substantially high transmission frequencies associated with RF communication increases the difficulty of miniaturization of the transmission components.
A major component of the cellular phone is the RF power amplifier thereof. Signal amplification requires corresponding power that generates heat in the amplifier which must be suitably dissipated for protecting the amplifier and associated electronic components.
The RF amplifier is conventionally in the form of a semiconductor integrated circuit (IC) chip or die in which power amplification is effected with substantial linearity. The amplifier chip must then be interconnected in a circuit with certain off-chip components such as inductors, capacitors, resistors, and transmission lines used for controlling operation of the amplifier chip and providing impedance matching of the input and output RF signals.
The amplifier chip and associated components are typically assembled on a printed circuit (PC) board in which the components are interconnected by printed metal circuits patterned atop a dielectric substrate. In a typical PC board, the chip and associated components are all mounted on one side of the board with the opposite, substrate-side of the board being exposed.
This single board configuration requires corresponding area over which the chip and components may be distributed. The board is typically rectangular and has a practical minimum size or surface area corresponding with the minimum sizes of the amplifier chip and required components.
Since the amplifier chip is mounted atop the PC board, the dielectric substrate thereof provides a thermally insulating barrier below the bottom of the chip, which chip requires suitable heat dissipation primarily from the top thereof. Since the PC amplifier board is mounted in a corresponding housing of the cellular phone in proximity to other electronic circuits therein, suitable accommodations must be provided for dissipating the heat and protecting the various electronic components thereof.
And, since RF circuits operate at high signal frequencies, electromagnetic radiation is created which can interfere with other components of the cellular phone, or with other electronic devices within the transmission range of the phone. Accordingly, a cellular phone require suitable shielding against electromagnetic interference (EMI) which affects the practical size of the phone.
RF signals are also subject to parasitic capacitance in the amplifier circuits which affects performance thereof. The relatively small distances between the RF amplifier and its associated components may experience not only parasitic capacitance but also differences in electrical potential between the components and ground which can also affect performance.
For example, the amplifier chip itself has an electrical ground which is correspondingly connected to an electrical ground of the printed circuit. The length or distance of the conducting path between the amplifier chip and ground, and between the PC components and ground may vary and correspondingly affect performance of the RF signal.
Yet another significant consideration in the miniaturization of RF amplifier circuits is the required impedance matching for the input and output RF signals of the amplifier. Input and output impedance matching circuits are conventional and typically include capacitors, resistors, and inductors in associated transmission lines for the RF signals into and out of the amplifier chip. However, these impedance matching circuits are specifically tailored in off-chip components and located remotely from the amplifier chip.
Accordingly, the amplifier chip itself must include many electrical input and output terminals or bonding pads to which the corresponding portions of the impedance matching circuits are separately joined. This increases the difficulty of assembly and required size of the associated amplifier components, and affects the overall marketability of the cellular phone.
It is therefore desired to provide a compact RF amplifier module having improved heat dissipation and integration of components.
An RF amplifier module includes PC boards laminated atop a bottom conductor plate. The boards include an RF semi-conductor amplifier chip mounted in a well extending to the bottom plate disposed in electrical connection with the chip.